A method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste

Abstract

This invention belongs to the technical field of iron-silicon-aluminum magnetic materials and provides a method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste. The method includes the following steps: powder preparation, proportioning, coating, granulation, pressing, and annealing. This invention uses silicon steel waste as raw material, which is smelted with ferrosilicon, aluminum ingots, ferrophosphorus, and electrolytic iron in a vacuum induction furnace and then powdered. The resulting iron-silicon-aluminum powder is then coated, granulated, pressed, and annealed to obtain the iron-silicon-aluminum magnetic powder core. This method achieves high-value utilization of silicon steel waste, significantly reduces raw material costs, and is environmentally friendly and energy-saving.

Description

Technical Field

[0001] This invention relates to a method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste, belonging to the technical field of iron-silicon-aluminum magnetic materials. Background Technology

[0002] Ferro-silicon-aluminum magnetic powder cores are an important type of metal magnetic powder cores, playing a crucial role in soft magnetic materials due to their low loss and low cost. Currently, ferro-silicon-aluminum magnetic powder cores are widely used in photovoltaic power generation systems (e.g., photovoltaic inverters), new energy vehicles (e.g., power conversion devices and on-board DC / DC converters), charging piles (e.g., PFC inductors), UPS power supplies (e.g., UPS inductors), and variable frequency air conditioners, among other fields.

[0003] Iron-silicon-aluminum magnetic powder cores are usually prepared by iron-silicon-aluminum powder through processes such as coating, pressing, and annealing. Iron-silicon-aluminum powder is usually obtained by mixing and melting high-purity elemental metals or alloys in a vacuum high-frequency induction furnace and then grinding them into powder. The raw material cost is relatively high and the energy consumption is relatively large.

[0004] Uncoated silicon steel (uncoated electrical steel) is a widely used soft magnetic material in the industrial, power, and electronics fields. It is currently widely used in the cores of various types of motors and generators. For example, Hunan Jinci New Material Technology Co., Ltd. disclosed a method for preparing uncoated semi-process electrical steel and its core in Chinese patent CN118957393A. The prepared uncoated semi-process electrical steel is pure and has high hardness, and its surface is free of chromium coating, making it more environmentally friendly. However, the preparation process of the uncoated electrical steel and its core in this patent generates a large amount of silicon steel waste (e.g., the slicing waste generated when preparing motor cores from uncoated semi-process electrical steel). Directly discarding this silicon steel waste would result in energy waste; therefore, it is necessary to recycle it. Currently, there are no reports on using silicon steel waste to prepare iron-silicon-aluminum magnetic powder cores. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, the purpose of this invention is to provide a method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste includes the following steps:

[0008] a) Powdering: 70-72 parts by weight of clean silicon steel waste, 12.0-12.8 parts by weight of ferrosilicon, 5.5-5.7 parts by weight of aluminum ingot, 0.2-0.4 parts by weight of ferrophosphorus, and 10-12 parts by weight of electrolytic iron are placed in a vacuum induction furnace for melting. Then, the mixture is atomized or mechanically crushed by a gas atomization device or a mechanical crushing device to obtain atomized iron-silicon-aluminum powder or crushed iron-silicon-aluminum powder. The silicon steel waste is the slicing waste generated when uncoated semi-process electrical steel is stamped and sliced ​​to prepare motor cores (specifically, the slicing waste generated when uncoated semi-process electrical steel is stamped and sliced ​​to prepare motor cores in patent "CN118957393A-A Method for Preparing Uncoated Semi-Process Electrical Steel and Cores").

[0009] b) Proportioning: The prepared gas-atomized iron-silicon-aluminum powder and crushed iron-silicon-aluminum powder are mixed in a mass ratio of 5:5-6:4 and then sieved according to particle size. Then, the particle size combination proportion is carried out as follows: 9-11wt% +200 mesh, 17-19wt% -200~+250 mesh, 31-33wt% -250~+325 mesh, 19-21wt% -325~+400 mesh, and 19-21wt% -400 mesh.

[0010] c) Coating: Add the prepared iron-silicon-aluminum powder to the coating solution, mix and stir at 55-65℃ for 20-40 minutes, filter, dry, and cool to room temperature to obtain coated powder. The coating solution consists of 0.6-1.0 parts by weight of phosphoric acid, 0.6-1.0 parts by weight of zinc acetate, 4-6 parts by weight of ethanol, and 9-11 parts by weight of deionized water. The amount of coating solution used is 14.2-19% of the mass of the iron-silicon-aluminum powder.

[0011] d) Granulation: The coating powder and binder are stirred at 65-75℃ until the powder and binder are completely mixed and dried. After cooling to room temperature, the mixture is sieved to obtain granulated powder. The binder is an organosilicon-acrylic hybrid emulsion, and the amount of binder added is 1-3% of the mass of the coating powder.

[0012] e) Pressing: After the granulated powder and lubricant are mixed evenly, press at 70-80 T / cm. 2 The material is pressed and molded under pressure, and after holding the pressure for 2-5 seconds, a blank magnetic core is obtained. The amount of lubricant added is 0.25-0.35% of the mass of the granulated powder.

[0013] f) Annealing: The blank magnetic core is placed in a hydrogen or nitrogen atmosphere for annealing treatment to obtain an iron-silicon-aluminum magnetic powder core.

[0014] In one embodiment, in step a), the ferrosilicon used is high-silicon ferrosilicon alloy FeSi75, the aluminum ingot used is industrial pure aluminum ingot A00, and the ferrophosphorus used is ferrophosphorus FeP24.

[0015] In one embodiment, step a) involves the preparation of the gas-atomized iron-silicon-aluminum powder and the crushed iron-silicon-aluminum powder, comprising the following steps:

[0016] 1) Crush, clean, and dry the silicon steel waste to obtain clean silicon steel waste, and weigh the proportions of silicon steel waste, ferrosilicon, aluminum ingots, ferrophosphorus and electrolytic iron.

[0017] 2) Place the proportioned amounts of silicon steel scrap, ferrosilicon, ferrophosphorus and electrolytic iron into a vacuum induction furnace, evacuate to <10Pa, and fill with high-purity argon until the gauge pressure inside the furnace is 0.02-0.05mPa. Melt at 1500-1600℃. After the furnace charge has basically melted, add aluminum ingots into the vacuum medium-frequency induction furnace for melting. After melting, let stand to remove slag and obtain molten alloy liquid.

[0018] 3) Transfer the molten alloy liquid to a preheated tundish and atomize it under a nitrogen pressure of 2.5-3.5 MPa to obtain spherical or near-spherical gas-atomized iron-silicon-aluminum powder;

[0019] Molten alloy liquid is poured into a preheated metal mold, cooled into ingots, and then subjected to homogenization annealing. The ingots are then crushed by a crusher to obtain irregularly shaped crushed iron-silicon-aluminum powder.

[0020] In a preferred embodiment, in step 2), the loading order of silicon steel scrap, ferrosilicon, ferrophosphorus and electrolytic iron is as follows: 2 / 3 of the silicon steel scrap and electrolytic iron are placed at the bottom, ferrosilicon and ferrophosphorus are placed in the middle, and the remaining 1 / 3 of the silicon steel scrap is placed at the top.

[0021] In a preferred embodiment, in step 2), when preparing gas-atomized iron-silicon-aluminum powder, silicon steel waste, ferrosilicon, ferrophosphorus and electrolytic iron are basically melted at 1550-1600℃, and then aluminum ingots are added to a vacuum medium-frequency induction furnace, kept warm and stirred for 5-10 minutes, and the aluminum ingots are completely melted by using the residual heat of the melt, and then allowed to stand to remove slag.

[0022] When preparing crushed iron-silicon-aluminum powder, first melt silicon steel waste, ferrosilicon, ferrophosphorus and electrolytic iron at 1500-1550℃, then cool down to 1450℃, add aluminum ingots into a vacuum medium-frequency induction furnace, keep warm and stir for 5-10 minutes to completely melt the aluminum ingots, and then let it stand to remove slag.

[0023] In a preferred embodiment, in step 3), the homogenization annealing treatment refers to holding at 1000-1100℃ for 4-10 hours and then cooling in the furnace.

[0024] In one embodiment, the iron-silicon-aluminum powder prepared in step b) is first heat-treated in a pure hydrogen or decomposed ammonia atmosphere for 1-3 hours at a temperature of 800-900℃, and then the heat-treated iron-silicon-aluminum powder is coated in step c).

[0025] In one embodiment, in step d), the preparation of the organosilicon-acrylic hybrid emulsion involves first performing an emulsion polymerization reaction on acrylic monomers to prepare an acrylic copolymer emulsion, and then in-situ grafting silanes and introducing modified nano-silica into the obtained acrylic copolymer emulsion to obtain the organosilicon-acrylic hybrid emulsion. The acrylic monomers are composed of methyl methacrylate (MMA), styrene (St), butyl acrylate (BA), hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA), and methacrylic acid (MAA). The silanes are γ-methacryloyloxypropyltrimethoxysilane (KH-570) and vinyltrimethoxysilane (A-171). The modified nano-silica is modified nano-silica obtained by modifying with octadecylamine.

[0026] In a preferred embodiment, the preparation of the organosilicon-acrylic hybrid emulsion includes the following steps:

[0027] ① Solution preparation:

[0028] Mix 2.8-3.2 parts by weight of sodium bicarbonate with 28-32 parts by weight of water until homogeneous to obtain a buffer solution;

[0029] Mix 7.8-8.2 parts by weight of ammonium persulfate with 78-82 parts by weight of water until homogeneous to obtain an initiator solution;

[0030] 20.5-21.5 parts by weight of γ-methacryloxypropyltrimethoxysilane, 8-9 parts by weight of vinyltrimethoxysilane, and 22-24 parts by weight of isopropanol are stirred and mixed evenly to obtain a silane mixture.

[0031] 14.5-15.5 parts by weight of octadecylamine-modified nano-silica stock solution with a solid content of 29-31% were mixed with 58-62 parts by weight of water to obtain a nano-dispersion.

[0032] ② Add 270-274 parts by weight of water, 8.5-9.5 parts by weight of reactive emulsifier SR-10, and 4-5 parts by weight of anionic emulsifier CO-436 to the emulsification tank, stir and mix evenly, then add 1.8-2.2 parts by weight of ammonia water to adjust the pH to 8.8-9.2, and then add 184-186 parts by weight of methyl methacrylate (MMA), 61-63 parts by weight of styrene (St), 109-111 parts by weight of butyl acrylate (BA), 12-13 parts by weight of hydroxyethyl methacrylate (HEMA), 12-13 parts by weight of glycidyl methacrylate (GMA), and 9-11 parts by weight of methacrylic acid (MAA) in sequence while stirring, and stir and mix evenly to obtain a pre-emulsion;

[0033] ③ Add 106-110 parts by weight of water and prepared buffer solution to the reaction vessel, stir and mix evenly, raise the temperature to 82°C under nitrogen protection, add 10% initiator solution and 10% pre-emulsion, keep the reaction at the temperature for 20-30 minutes to obtain seed emulsion.

[0034] ④ Heat to 84℃, slowly add the remaining 90% of the initiator solution and the remaining 90% of the pre-emulsion, maintaining the pH of the system at 7.8-8.5 during the addition process. After the addition is complete, continue to keep the temperature and react for 30-60 minutes to obtain acrylic copolymer emulsion.

[0035] ⑤ Cool down to 76℃, slowly add silane mixture dropwise, maintain the pH of the system at 7.8-8.2 during the dropwise addition, continue to keep the temperature and react for 10-20 minutes after the dropwise addition is complete, then slowly add nano dispersion dropwise, raise the temperature to 85℃ after the dropwise addition is complete, and keep the temperature and react for 2-3 hours after the dropwise addition is complete.

[0036] ⑥ Cool to 40℃, add 3-3.4 parts by weight of defoamer, stir and mix evenly, then add 3-3.4 parts by weight of preservative, stir and mix evenly, filter, and mature to obtain organosilicon acrylic hybrid emulsion.

[0037] In a preferred embodiment, in step ①, the preparation of the octadecylamine-modified nano-silica stock solution involves first generating nano-silica sol in situ via a sol-gel method, and then using octadecylamine to perform surface hydrophobic modification to obtain a stable and dispersed hydrophobic aqueous nano-silica dispersion, which is the octadecylamine-modified nano-silica stock solution. Specifically, the process includes the following steps:

[0038] Add 38-42 parts by mass of water and 9-10 parts by mass of ammonia to the reactor, adjust the pH of the system to 11, and heat to 50°C to obtain an alkaline solution.

[0039] 29-31 parts by weight of tetraethyl orthosilicate and 14-16 parts by weight of anhydrous ethanol are stirred and mixed evenly. The resulting tetraethyl orthosilicate-ethanol mixture is added dropwise to an alkaline solution. During the dropwise addition, the pH of the system is maintained at 10.5-11.5. After the dropwise addition is completed, the temperature is raised to 60°C and stirred for 2-4 hours to obtain nano-silica sol.

[0040] Mix 2-2.4 parts by weight of KH-560 with 4.5-5.5 parts by weight of anhydrous ethanol until homogeneous, add 0.8-1.2 parts by weight of water, and stir at room temperature for 20-40 minutes to hydrolyze and obtain KH-560 hydrolysate; mix 1.8-2.0 parts by weight of octadecylamine with 9-11 parts by weight of anhydrous ethanol, and stir at 70°C until completely clear and transparent to obtain octadecylamine ethanol solution;

[0041] KH-560 hydrolysate was slowly added to the nano-silica sol. After the addition was complete, the reaction was continued at 60°C for 0.5-1.5 hours. Then, octadecylamine ethanol solution was slowly added dropwise. After the addition was complete, the temperature was raised to 70°C and the reaction was maintained for 5-6 hours. The reaction was then stopped. The resulting reaction solution was distilled under reduced pressure to remove the ethanol. Then, the temperature was lowered to 50°C, and 19-21 parts by weight of water were added. The mixture was stirred and maintained at this temperature for 0.5-1.5 hours. The pH of the system was adjusted to 9.5-10.0. The solution was cooled to room temperature, homogenized, and filtered to obtain the octadecylamine-modified nano-silica stock solution.

[0042] In a preferred embodiment, in step ⑥, the defoamer is defoamer BYK-019 and the preservative is preservative Acticide MBS.

[0043] In one embodiment, in step e), the lubricant is a stearate lubricant, and the stearate is any one of zinc stearate, magnesium stearate, and barium stearate.

[0044] In one implementation scheme, in step f), the annealing temperature is 600-800℃ and the annealing time is 1-3 hours.

[0045] Compared with the prior art, the present invention has the following significant advantages:

[0046] This invention uses silicon steel waste as raw material, which is smelted in a vacuum induction furnace with ferrosilicon, aluminum ingots, ferrophosphorus, and electrolytic iron to produce powder. The resulting iron-silicon-aluminum powder is then coated, granulated, pressed, and annealed to obtain an iron-silicon-aluminum magnetic powder core. This invention achieves high-value utilization of silicon steel waste, significantly reduces raw material costs, and is environmentally friendly and energy-saving. Attached Figure Description

[0047] Figure 1 The image shows the gas-atomized iron-silicon-aluminum powder prepared in an embodiment of the present invention.

[0048] Figure 2 The image shows the crushed iron-silicon-aluminum powder prepared in an embodiment of the present invention.

[0049] Figure 3 This is a VSM analysis result diagram of the gas-atomized iron-silicon-aluminum powder prepared in the embodiments of the present invention;

[0050] Figure 4 This is a diagram showing the result of pressing granulated powder into an iron-silicon-aluminum magnetic powder core in Example 1 of the present invention.

[0051] Figure 5 This is a diagram showing the result of pressing the granulated powder into an iron-silicon-aluminum magnetic powder core in Comparative Example 1 of the present invention. Detailed Implementation

[0052] The technical solution of the present invention will be further described in detail and completely below with reference to the embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer.

[0053] Example 1

[0054] 1) Preparation of organosilicon-acrylic hybrid emulsion

[0055] ① Solution preparation:

[0056] 3 parts by mass of sodium bicarbonate and 30 parts by mass of water were stirred and mixed evenly to obtain a buffer solution; 8 parts by mass of ammonium persulfate and 80 parts by mass of water were stirred and mixed evenly to obtain an initiator solution; 21 parts by mass of γ-methacryloyloxypropyltrimethoxysilane, 8.5 parts by mass of vinyltrimethoxysilane and 23 parts by mass of isopropanol were stirred and mixed evenly to obtain a silane mixture.

[0057] 15 parts by weight of octadecylamine-modified nano-silica stock solution with a solid content of 30% were mixed with 60 parts by weight of water to obtain a nano-dispersion; wherein, the preparation of the octadecylamine-modified nano-silica stock solution includes the following operations:

[0058] Add 40 parts by mass of water and 9.5 parts by mass of ammonia to the reactor, adjust the pH of the system to 11, and heat to 50°C to obtain an alkaline solution.

[0059] 30 parts by mass of tetraethyl orthosilicate and 15 parts by mass of anhydrous ethanol were stirred and mixed evenly. The resulting tetraethyl orthosilicate-ethanol mixture was added dropwise to an alkaline solution over a period of approximately 45 minutes. During the addition process, the pH of the system was maintained at 10.5-11.5. After the addition was completed, the temperature was raised to 60°C and stirred for 2-4 hours to obtain nano-silica sol.

[0060] Mix 2.2 parts by mass of KH-560 with 5 parts by mass of anhydrous ethanol until homogeneous, add 1 part by mass of water, and stir at room temperature for 30 minutes to hydrolyze and obtain KH-560 hydrolysate; mix 1.9 parts by mass of octadecylamine with 10 parts by mass of anhydrous ethanol, and stir at 70°C until completely clear and transparent to obtain octadecylamine ethanol solution.

[0061] KH-560 hydrolysate was slowly added to the nano-silica sol over a period of approximately 20 minutes. After the addition was complete, the reaction was maintained at 60°C for 1 hour. Then, octadecylamine ethanol solution was slowly added dropwise. After the addition was complete, the temperature was raised to 70°C and the reaction was maintained for 5.5 hours. The reaction was then stopped. The resulting reaction solution was distilled under reduced pressure to remove the ethanol. The solution was then cooled to 50°C, and 20 parts by mass of water were added. The solution was stirred and maintained at this temperature for 1 hour. The pH of the system was adjusted to 9.5-10.0. The solution was cooled to room temperature, homogenized, and filtered to obtain an octadecylamine-modified nano-silica stock solution with a solid content of approximately 30%.

[0062] ② Add 272 parts by weight of water, 9 parts by weight of reactive emulsifier SR-10, and 4.5 parts by weight of anionic emulsifier CO-436 to the emulsification tank, stir and mix evenly, then add 2 parts by weight of ammonia water to adjust the pH to 8.8-9.2, and then add 185 parts by weight of methyl methacrylate (MMA), 62 parts by weight of styrene (St), 110 parts by weight of butyl acrylate (BA), 12.5 parts by weight of hydroxyethyl methacrylate (HEMA), 12.5 parts by weight of glycidyl methacrylate (GMA), and 10 parts by weight of methacrylic acid (MAA) in sequence while stirring, and stir and mix evenly to obtain a milky white pre-emulsion;

[0063] ③ Add 108 parts by mass of water and the prepared buffer solution to the reaction vessel, stir and mix evenly, raise the temperature to 82°C under nitrogen protection, add 10% initiator solution and 10% pre-emulsion, keep the reaction at the temperature for 25 minutes to obtain seed emulsion;

[0064] ④ Heat to 84℃, slowly add the remaining 90% of the initiator solution and the remaining 90% of the pre-emulsion solution, with a dropping time of about 215 minutes. During the dropping process, maintain the pH of the system at 7.8-8.5. After the dropping is completed, continue to keep the temperature and react for 45 minutes to obtain acrylic copolymer emulsion.

[0065] ⑤ Cool down to 76℃, slowly add the silane mixture dropwise over a period of about 60 minutes, maintaining the pH of the system at 7.8-8.2 during the dropwise addition. After the dropwise addition is complete, continue to keep the temperature and react for 15 minutes. Then slowly add the nano-dispersion dropwise over a period of about 60 minutes. After the dropwise addition is complete, raise the temperature to 85℃ and keep the temperature and react for 2.5 hours.

[0066] ⑥ Cool to 40℃, add 3.2 parts by weight of defoamer BYK-019, stir and mix evenly, then add 3.2 parts by weight of preservative Acticide MBS, stir and mix evenly, filter (filter through a 200-mesh sieve), and mature for 24 hours to obtain an organosilicon acrylic hybrid emulsion with a solid content of about 50%.

[0067] (ii) Preparation of iron-silicon-aluminum granulated powder

[0068] a) Flour making:

[0069] The preparation of gas-atomized iron-silicon-aluminum powder includes the following steps:

[0070] 1) The silicon steel waste (specifically the slicing waste generated during the preparation of motor cores from uncoated semi-process electrical steel stamping and slicing as described in patent "CN118957393A - A method for preparing uncoated semi-process electrical steel and iron core") is crushed, cleaned, and dried to obtain clean silicon steel waste. The proportions of silicon steel waste, ferrosilicon, aluminum ingots, ferrophosphorus, and electrolytic iron are weighed, specifically: 71.4 parts by mass of clean silicon steel waste, 12.6 parts by mass of ferrosilicon FeSi75, 5.67 parts by mass of aluminum ingot A00, 0.264 parts by mass of ferrophosphorus FeP24, and 10.1 parts by mass of electrolytic iron;

[0071] 2) Place the required proportions of silicon steel scrap, ferrosilicon, ferrophosphorus, and electrolytic iron into a vacuum induction furnace. The loading order is as follows: place approximately 2 / 3 of the required proportions of silicon steel scrap and all of the required proportions of electrolytic iron at the bottom, place all of the required proportions of ferrosilicon and ferrophosphorus in the middle, and place the remaining 1 / 3 of the required proportions of silicon steel scrap at the top. Then, evacuate the furnace to <10Pa, and fill it with high-purity argon until the gauge pressure inside the furnace is 0.03mPa. Melt the furnace at 1550℃. After the furnace charge has basically melted, add the required proportions of aluminum ingots into the vacuum medium-frequency induction furnace for melting. Keep the furnace at this temperature and stir for 10 minutes. Use the residual heat of the melt to completely melt the aluminum ingots. Then, let the furnace stand to remove slag and obtain a molten alloy liquid.

[0072] 3) Transfer the molten alloy liquid to a preheating tundish and atomize it under a nitrogen pressure of 3MPa to obtain gas-atomized iron-silicon-aluminum powder;

[0073] The preparation of crushed iron-silicon-aluminum powder includes the following steps:

[0074] 1) The silicon steel waste (specifically, the slicing waste generated during the stamping and slicing of uncoated semi-process electrical steel to prepare motor cores in patent "CN118957393A-A Method for Preparing Uncoated Semi-Process Electrical Steel and Cores") is crushed, cleaned, and dried to obtain clean silicon steel waste. The proportions of silicon steel waste, ferrosilicon, aluminum ingots, ferrophosphorus, and electrolytic iron are weighed, specifically: 70.0 parts by weight of clean silicon steel waste, 12.4 parts by weight of ferrosilicon FeSi75, 5.6 parts by weight of aluminum ingot A00, 0.3 parts by weight of ferrophosphorus FeP24, and 11.7 parts by weight of electrolytic iron (the preparation processes of gas-atomized iron-silicon-aluminum powder and crushed iron-silicon-aluminum powder are different, so the raw material proportions are also different).

[0075] 2) Place the required proportions of silicon steel scrap, ferrosilicon, ferrophosphorus, and electrolytic iron into a vacuum induction furnace. The loading order is as follows: place approximately 2 / 3 of the required proportions of silicon steel scrap and all of the required proportions of electrolytic iron at the bottom, place all of the required proportions of ferrosilicon and ferrophosphorus in the middle, and place the remaining 1 / 3 of the required proportions of silicon steel scrap at the top. Then, evacuate the furnace to <10Pa, and fill it with high-purity argon until the gauge pressure inside the furnace is 0.03mPa. Melt the furnace at 1500℃. After the furnace charge has basically melted, cool the furnace to 1450℃ and add the required proportions of aluminum ingots into the vacuum medium-frequency induction furnace for melting. Hold the furnace at this temperature and stir for 10 minutes to completely melt the aluminum ingots. Then, allow the furnace to stand to remove slag and obtain a molten alloy liquid.

[0076] 3) Pour the molten alloy liquid into a preheated metal mold, cool it into an ingot, perform homogenization annealing on the ingot, and then crush it with a crusher to obtain crushed iron-silicon-aluminum powder;

[0077] b) Proportioning: The prepared gas-atomized iron-silicon-aluminum powder and crushed iron-silicon-aluminum powder are mixed at a mass ratio of 5:5 and then sieved according to particle size. Then, the particle size combination proportion is carried out as follows: 10wt% +200 mesh, 18wt% -200~+250 mesh, 32wt% -250~+325 mesh, 20wt% -325~+400 mesh, and 20wt% -400 mesh.

[0078] c) Coating: 100 parts by weight of the prepared iron-silicon-aluminum powder are added to the coating solution, mixed and stirred at 60°C for 30 minutes, filtered, dried in a vacuum drying oven at 80°C, and cooled to room temperature to obtain coated powder. The coating solution is composed of 0.94 parts by weight of 85% phosphoric acid, 0.8 parts by weight of zinc acetate, 5 parts by weight of ethanol and 10 parts by weight of deionized water.

[0079] d) Granulation: 100 parts by weight of the coated powder and 2 parts by weight of a self-made organosilicon-acrylic hybrid emulsion with a solid content of approximately 50% are stirred at 70°C until the powder and organosilicon-acrylic hybrid emulsion are completely mixed. After drying, the mixture is cooled to room temperature and passed through a 200-mesh sieve to obtain granulated powder.

[0080] e) Pressing: After the granulated powder and the lubricant zinc stearate are mixed evenly, press at 75T / cm 2 The material is pressed and molded under pressure, and after holding the pressure for 5 seconds, a blank magnetic core is obtained. The amount of lubricant added is 0.25% of the mass of the granulated powder.

[0081] f) Annealing: The blank magnetic core is placed in a nitrogen atmosphere for annealing treatment. The annealing temperature is 700℃ and the annealing time is 2 hours to obtain an iron-silicon-aluminum magnetic powder core.

[0082] Figure 1 Images of the gas-atomized iron-silicon-aluminum powder prepared in this embodiment are shown below. Figure 1As can be seen, the gas-atomized iron-silicon-aluminum powder prepared in this embodiment has a spherical or near-spherical structure.

[0083] Figure 2 The image shows the crushed iron-silicon-aluminum powder prepared in this embodiment. Figure 2 As can be seen, the crushed iron-silicon-aluminum powder prepared in this embodiment is irregular in shape.

[0084] The gas-atomized iron-silicon-aluminum powder prepared in this embodiment was tested using a vibrating sample magnetometer (VSM) with a Lake Shore-8604 (USA). The test results are as follows: Figure 3 As shown, from Figure 3 As can be seen, the iron-silicon-aluminum powder prepared in this embodiment has excellent magnetic properties. The VSM test results of the crushed iron-silicon-aluminum powder are similar to those of the gas-atomized iron-silicon-aluminum powder, and are omitted here.

[0085] Chemical analysis was performed on the gas-atomized iron-silicon-aluminum powder prepared in this embodiment. Each element was tested according to the following standards: O and S according to ASTM E1019-24; Al according to NACIS / CH 008:2023; Si according to NACIS / CH 009:2013R1; B, Cr, Mn, and P according to NACIS / CH 011:2024; Fe according to NACIS / CH 143:2015. The analysis results showed that the iron-silicon-aluminum powder prepared in this embodiment contained 83.88% Fe, 9.45% Si, 5.67% Al, 0.0013% S, 0.021% O, 0.0035% B, 0.072% P, 0.25% Mn, and 0.032% Cr. The chemical analysis results of the crushed iron-silicon-aluminum powder were similar to those of the gas-atomized iron-silicon-aluminum powder and are omitted here.

[0086] Figure 4 This is a diagram showing the result of pressing the granulated powder into an iron-silicon-aluminum magnetic powder core in step e) of this embodiment. Figure 4 It can be seen that the iron-silicon-aluminum granulated powder prepared in this embodiment can be pressed into iron-silicon-aluminum magnetic powder cores.

[0087] Example 2

[0088] The difference between this embodiment and Embodiment 1 is that:

[0089] In step b), the prepared gas-atomized iron-silicon-aluminum powder and crushed iron-silicon-aluminum powder are mixed at a mass ratio of 6:4 and then sieved according to particle size.

[0090] In step e), at 80T / cm 2 It is pressed and molded under pressure, with a holding time of 2 seconds, and the amount of lubricant added is 0.35% of the mass of the granulated powder;

[0091] The remaining conditions are the same as in Example 1.

[0092] In step e), the result of pressing the granulated powder into an iron-silicon-aluminum magnetic powder core is also as follows. Figure 4 As shown, the iron-silicon-aluminum granulated powder prepared in this embodiment can also be pressed into iron-silicon-aluminum magnetic powder cores.

[0093] Comparative Example 1

[0094] The difference between this comparative example and Example 1 is as follows:

[0095] In step b), the iron-silicon-aluminum powder used is pure gas-atomized iron-silicon-aluminum, which does not contain crushed iron-silicon-aluminum powder;

[0096] The coating solution used in step c) does not contain zinc acetate;

[0097] In step d), the binder used during granulation is a pure silicone emulsion. Specifically, the preparation method of the silicone emulsion is as follows:

[0098] ① Solution preparation:

[0099] 3 parts by mass of sodium bicarbonate and 30 parts by mass of water were stirred and mixed evenly to obtain a buffer solution; 8 parts by mass of ammonium persulfate and 80 parts by mass of water were stirred and mixed evenly to obtain an initiator solution; 210 parts by mass of γ-methacryloyloxypropyltrimethoxysilane, 85 parts by mass of vinyltrimethoxysilane and 230 parts by mass of isopropanol were stirred and mixed evenly to obtain a silane mixture.

[0100] ② Add 250 parts by weight of water, 9 parts by weight of reactive emulsifier SR-10, and 4.5 parts by weight of anionic emulsifier CO-436 to the emulsification kettle, stir and mix evenly, then add 8 parts by weight of ammonia water, adjust the pH to 10.5-11.0, stir until the emulsifier is completely dissolved, then add the silane mixture while stirring. After the addition is completed, perform high-speed shear emulsification for 45 minutes (stirring speed is 2000 rpm) to obtain a milky white pre-emulsion.

[0101] ③ Add 130 parts by weight of water and the prepared buffer solution to the reaction vessel, stir and mix evenly, raise the temperature to 82°C under nitrogen protection, add 10% initiator solution and 10% pre-emulsion, keep the temperature and react for 40 minutes to obtain seed emulsion.

[0102] ④ Heat to 84℃, slowly add the remaining 90% of the initiator solution and the remaining 90% of the pre-emulsion solution dropwise over a period of approximately 240 minutes. Maintain the pH of the system at 10.0-10.8 during the dropwise addition. After the dropwise addition is complete, continue to keep the system at the temperature for 4.5 hours.

[0103] ⑤ Cool to 40℃, add 3.2 parts by weight of defoamer BYK-019, stir and mix evenly, then add 3.2 parts by weight of preservative Acticide MBS, stir and mix evenly, add acetic acid to adjust the pH of the system to 7.5-8.0, filter (200 mesh sieve), and mature for 24 hours to obtain an organosilicon emulsion with a solid content of about 50%.

[0104] The remaining conditions are the same as in Example 1.

[0105] Figure 5 This is a diagram showing the result of pressing the granulated powder into an iron-silicon-aluminum magnetic powder core in step e) of this comparative example. Figure 5 It is evident that the iron-silicon-aluminum granulated powder prepared in this comparative example cannot be pressed into shape, thus failing to produce the desired iron-silicon-aluminum magnetic powder core.

[0106] As can be seen from Examples 1-2 and Comparative Example 1, only the preparation process described in the examples can be used to prepare iron-silicon-aluminum magnetic powder cores from silicon steel waste. Changing the composition of the iron-silicon-aluminum powder, the composition of the coating liquid, and the composition of the binder during granulation will cause the granulated powder to be unable to be pressed into shape, thus making it impossible to obtain the desired iron-silicon-aluminum magnetic powder core. This is because:

[0107] The iron-silicon-aluminum powder used in Examples 1-2 is obtained by mixing gas-atomized iron-silicon-aluminum powder and crushed iron-silicon-aluminum powder in a mass ratio of 5:5-6:4. The crushed iron-silicon-aluminum powder has an irregular shape, which helps the particles to mechanically interlock and stack, improves the strength of the pressed blank, and thus helps with pressing and molding. In contrast, the iron-silicon-aluminum powder used in Comparative Example 1 is pure gas-atomized iron-silicon-aluminum powder. Although the spherical gas-atomized iron-silicon-aluminum powder has good flowability, the particles mainly rely on point contact during pressing. It lacks the "bridging" and filling effect of the irregular crushed iron-silicon-aluminum powder, and the bonding force between particles is weak, which easily leads to loose pressed blanks and insufficient strength, which is not conducive to pressing and molding.

[0108] In Examples 1-2, the coating solution used during coating contained phosphoric acid and zinc acetate, which gave the coated powder a certain degree of adhesion and passivation, which was beneficial for the subsequent adhesion of organic binders and thus facilitated compression molding. In contrast, the coating solution used in Comparative Example 1 did not contain zinc acetate, resulting in high surface activity of the powder, easy oxidation, or poor bonding with the binder, leading to poor bonding force during subsequent granulation powder compression, which was not conducive to compression molding.

[0109] In Examples 1-2, the binder used during granulation was a self-made organosilicon acrylic emulsion containing acrylic monomer copolymer and silane-modified nano-silica. It has high film-forming properties, flexibility, and bonding strength, and the nanoparticles can enhance interfacial bonding, thus facilitating the pressing and molding of the granulated powder. In contrast, the binder used during granulation in Comparative Example 1 was an ordinary organosilicon emulsion, which has brittle film-forming properties and insufficient bonding strength. This makes it easy for the organic layer between particles to break during the pressing of the granulated powder, making it impossible to maintain the integrity of the green body, which is not conducive to pressing and molding.

[0110] Comparative Example 2

[0111] The difference between this comparative example and Example 1 is as follows:

[0112] In step b), the prepared gas-atomized iron-silicon-aluminum powder and crushed iron-silicon-aluminum powder are mixed at a mass ratio of 9:1 and then sieved according to particle size to obtain gas-atomized iron-silicon-aluminum powder and crushed iron-silicon-aluminum powder of different particle sizes. Then, the particle size combination ratio is carried out as follows: 5wt% +200 mesh, 10wt% -200~+250 mesh, 25wt% -250~+325 mesh, 20wt% -325~+400 mesh, and 40wt% -400 mesh.

[0113] The coating solution used in step c) does not contain zinc acetate;

[0114] The binder used in step d) during granulation is the pure organosilicon emulsion from Comparative Example 1;

[0115] In step e), the holding time during compression is 0.5 seconds;

[0116] The remaining conditions are the same as in Preliminary Example 1.

[0117] The iron-silicon-aluminum granulated powder prepared in this comparative example, like that in Comparative Example 1, could not be pressed into shape, thus failing to produce the desired iron-silicon-aluminum magnetic powder core.

[0118] As can be seen from Examples 1-2 and Comparative Examples 1-2, only the preparation process described in the examples can be used to prepare iron-silicon-aluminum magnetic powder cores from silicon steel waste. Besides changing the composition of the iron-silicon-aluminum powder, the composition of the coating liquid, and the composition of the binder during granulation, changing the particle size distribution and holding time of the iron-silicon-aluminum powder will also prevent the granulated powder from being pressed into shape, thus failing to obtain the desired iron-silicon-aluminum magnetic powder core. This is because:

[0119] The iron-silicon-aluminum powder used in the examples is obtained by mixing gas-atomized iron-silicon-aluminum powder and crushed iron-silicon-aluminum powder in a mass ratio of 5:5-6:4. The crushed iron-silicon-aluminum powder has an irregular shape, which helps the particles to mechanically interlock and stack, improves the strength of the pressed blank, and thus helps with pressing and molding. In contrast, although the iron-silicon-aluminum powder used in Comparative Example 2 contains crushed iron-silicon-aluminum powder, the content of crushed iron-silicon-aluminum powder is low, and it is still mainly composed of spherical gas-atomized iron-silicon-aluminum powder, resulting in weak bonding force between particles, which is not conducive to pressing and molding.

[0120] In Examples 1-2, the iron-silicon-aluminum powder particle size distribution is reasonable, with fine and coarse powders evenly distributed, resulting in good overall particle flowability and interlocking ability, which is conducive to pressing and molding. In contrast, in Comparative Example 2, the iron-silicon-aluminum powder particle size distribution is unreasonable, with an excessive proportion of fine powder, leading to poor particle flowability, uneven filling, uneven pressing density distribution, high inter-particle friction, stress concentration during pressing, weak interlocking ability between particles, and difficulty in forming a stable skeleton, ultimately hindering pressing and molding.

[0121] In Examples 1-2, the holding time during pressing is 2-5 seconds, which is sufficient to allow the powder particles to flow and adjust their positions, resulting in good structural stability. Simultaneously, both the lubricant and the binder on the surface of the granulated powder can fully function, aiding in pressing and molding. In contrast, in Comparative Example 2, the holding time is insufficient, causing the powder particles to not have enough time to flow and adjust their positions under pressure, failing to fill the gaps between particles. This results in numerous "voids" inside the green body, leading to extremely poor structural stability. Furthermore, the lubricant cannot form a uniform lubricating film on the particle surface, thus failing to reduce inter-particle friction and aiding particle sliding. The binder on the surface of the granulated powder cannot fully solidify to form a "bonding network," failing to connect the dispersed particles into a whole. Ultimately, neither the lubricant nor the binder can function effectively, hindering pressing and molding.

[0122] Performance testing

[0123] The performance of the iron-silicon-aluminum magnetic powder cores prepared in Examples 1 and 2 was tested, specifically as follows:

[0124] The initial permeability (μi) was measured using an impedance analyzer at 10 kHz and 0.1 mT, in accordance with IEC 60401-3:2022.

[0125] Magnetic loss (Pcv, kW / m³) was tested at 100 kHz and 100 mT according to IEC60404-6:2018.

[0126] Referring to IPCTM-650 2.5.13, the permeability retention rate was measured under a DC bias magnetic field of 100 Oe, thereby measuring the DC superposition performance;

[0127] The test results are shown in Table 1.

[0128] Table 1 Performance test data of the iron-silicon-aluminum magnetic powder cores prepared in Examples 1 and 2

[0129]

[0130] As shown in Table 1, the iron-silicon-aluminum magnetic powder prepared by the method described in the embodiments of the present invention has high magnetic permeability, low magnetic loss and good DC superposition performance.

[0131] In summary, this invention uses silicon steel waste as raw material, which is then smelted with ferrosilicon, aluminum ingots, ferrophosphorus, and electrolytic iron in a vacuum induction furnace and pulverized. The resulting iron-silicon-aluminum powder is coated, granulated, pressed, and annealed to obtain an iron-silicon-aluminum magnetic powder core. This achieves high-value utilization of silicon steel waste, significantly reduces raw material costs, and is environmentally friendly and energy-saving.

[0132] Finally, it should be noted that the above are only some preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste, characterized in that, Includes the following steps: a) Powdering: 70-72 parts by weight of clean silicon steel waste, 12.0-12.8 parts by weight of ferrosilicon, 5.5-5.7 parts by weight of aluminum ingot, 0.2-0.4 parts by weight of ferrophosphorus, and 10-12 parts by weight of electrolytic iron are placed in a vacuum induction furnace for melting. Then, the mixture is atomized or mechanically crushed by a gas atomization device or a mechanical crushing device to obtain gas-atomized iron-silicon-aluminum powder or crushed iron-silicon-aluminum powder. The silicon steel waste is the slicing waste generated when uncoated semi-process electrical steel is stamped and sliced ​​to prepare motor cores. b) Proportioning: The prepared gas-atomized iron-silicon-aluminum powder and crushed iron-silicon-aluminum powder are mixed in a mass ratio of 5:5-6:4 and then sieved according to particle size. Then, the particle size combination proportion is carried out as follows: 9-11wt% +200 mesh, 17-19wt% -200~+250 mesh, 31-33wt% -250~+325 mesh, 19-21wt% -325~+400 mesh, and 19-21wt% -400 mesh. c) Coating: Add the prepared iron-silicon-aluminum powder to the coating solution, mix and stir at 55-65℃ for 20-40 minutes, filter, dry, and cool to room temperature to obtain coated powder. The coating solution consists of 0.6-1.0 parts by weight of phosphoric acid, 0.6-1.0 parts by weight of zinc acetate, 4-6 parts by weight of ethanol, and 9-11 parts by weight of deionized water. The amount of coating solution used is 14.2-19% of the mass of the iron-silicon-aluminum powder. d) Granulation: The coating powder and binder are stirred at 65-75℃ until the powder and binder are completely mixed and dried. After cooling to room temperature, the mixture is sieved to obtain granulated powder. The binder is an organosilicon-acrylic hybrid emulsion, and the amount of binder added is 1-3% of the mass of the coating powder. e) pressing: the granulated powder is mixed with lubricant and uniformly pressed into a shape under the pressure of 70-80T / cm 2 after 2-5 seconds of pressure keeping, a rough core is obtained, the added amount of the lubricant is 0.25-0.35% of the mass of the granulated powder; f) Annealing: The blank magnetic core is placed in a hydrogen or nitrogen atmosphere for annealing to obtain an iron-silicon-aluminum magnetic powder core. In step b), the prepared iron-silicon-aluminum powder is first heat-treated in a pure hydrogen or decomposed ammonia atmosphere for 1-3 hours at a temperature of 800-900℃. The heat-treated iron-silicon-aluminum powder is then coated in step c). In step d), the preparation of the organosilicon-acrylic hybrid emulsion involves first performing an emulsion polymerization reaction on acrylic monomers to prepare an acrylic copolymer emulsion, and then in-situ grafting silanes and introducing modified nano-silica into the obtained acrylic copolymer emulsion to obtain the organosilicon-acrylic hybrid emulsion. The acrylic monomers are composed of methyl methacrylate, styrene, butyl acrylate, hydroxyethyl methacrylate, glycidyl methacrylate, and methacrylic acid. The silanes are γ-methacryloyloxypropyltrimethoxysilane and vinyltrimethoxysilane. The modified nano-silica is modified nano-silica obtained by modifying with octadecylamine.

2. The method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste according to claim 1, characterized in that, In step a), the preparation of the gas-atomized iron-silicon-aluminum powder and the crushed iron-silicon-aluminum powder includes the following steps: 1) Crush, clean, and dry the silicon steel waste to obtain clean silicon steel waste, and weigh the proportions of silicon steel waste, ferrosilicon, aluminum ingots, ferrophosphorus and electrolytic iron. 2) Place the proportioned amounts of silicon steel scrap, ferrosilicon, ferrophosphorus and electrolytic iron into a vacuum induction furnace, evacuate to <10Pa, and fill with high-purity argon until the gauge pressure inside the furnace is 0.02-0.05mPa. Melt at 1500-1600℃. After the furnace charge has basically melted, add aluminum ingots into the vacuum medium-frequency induction furnace for melting. After melting, let stand to remove slag and obtain molten alloy liquid. 3) Transfer the molten alloy liquid to a preheated tundish and atomize it under a nitrogen pressure of 2.5-3.5 MPa to obtain spherical or near-spherical gas-atomized iron-silicon-aluminum powder; Molten alloy liquid is poured into a preheated metal mold, cooled into ingots, and then subjected to homogenization annealing. The ingots are then crushed by a crusher to obtain irregularly shaped crushed iron-silicon-aluminum powder.

3. The method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste according to claim 2, characterized in that, In step 2), the loading order of silicon steel scrap, ferrosilicon, ferrophosphorus and electrolytic iron is as follows: 2 / 3 of the silicon steel scrap and electrolytic iron are placed at the bottom, ferrosilicon and ferrophosphorus are placed in the middle, and the remaining 1 / 3 of the silicon steel scrap is placed at the top.

4. The method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste according to claim 2, characterized in that, In step 2), when preparing gas-atomized iron-silicon-aluminum powder, the silicon steel waste, ferrosilicon, ferrophosphorus and electrolytic iron are basically melted at 1550-1600℃. Then, the aluminum ingot is added to the vacuum medium-frequency induction furnace, kept warm and stirred for 5-10 minutes, and the aluminum ingot is completely melted by using the residual heat of the melt. Then, it is allowed to stand to remove slag. When preparing crushed iron-silicon-aluminum powder, first melt silicon steel waste, ferrosilicon, ferrophosphorus and electrolytic iron at 1500-1550℃, then cool down to 1450℃, add aluminum ingots into a vacuum medium-frequency induction furnace, keep warm and stir for 5-10 minutes to completely melt the aluminum ingots, and then let it stand to remove slag.

5. The method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste according to claim 2, characterized in that, In step 3), the homogenization annealing treatment refers to holding at 1000-1100℃ for 4-10 hours and then cooling in the furnace.

6. The method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste according to claim 1, characterized in that, The preparation of the organosilicon-acrylic hybrid emulsion includes the following steps: ① Solution preparation: Mix 2.8-3.2 parts by weight of sodium bicarbonate with 28-32 parts by weight of water until homogeneous to obtain a buffer solution; Mix 7.8-8.2 parts by weight of ammonium persulfate with 78-82 parts by weight of water until homogeneous to obtain an initiator solution; 20.5-21.5 parts by weight of γ-methacryloxypropyltrimethoxysilane, 8-9 parts by weight of vinyltrimethoxysilane, and 22-24 parts by weight of isopropanol are stirred and mixed evenly to obtain a silane mixture. 14.5-15.5 parts by weight of octadecylamine-modified nano-silica stock solution with a solid content of 29-31% were mixed with 58-62 parts by weight of water to obtain a nano-dispersion. ② Add 270-274 parts by weight of water, 8.5-9.5 parts by weight of reactive emulsifier SR-10, and 4-5 parts by weight of anionic emulsifier CO-436 to the emulsification tank, stir and mix evenly, then add 1.8-2.2 parts by weight of ammonia water to adjust the pH to 8.8-9.2, and then add 184-186 parts by weight of methyl methacrylate, 61-63 parts by weight of styrene, 109-111 parts by weight of butyl acrylate, 12-13 parts by weight of hydroxyethyl methacrylate, 12-13 parts by weight of glycidyl methacrylate, and 9-11 parts by weight of methacrylic acid in sequence while stirring, and stir and mix evenly to obtain a pre-emulsion; ③ Add 106-110 parts by weight of water and prepared buffer solution to the reaction vessel, stir and mix evenly, raise the temperature to 82°C under nitrogen protection, add 10% initiator solution and 10% pre-emulsion, keep the reaction at the temperature for 20-30 minutes to obtain seed emulsion. ④ Heat to 84℃, slowly add the remaining 90% of the initiator solution and the remaining 90% of the pre-emulsion, maintaining the pH of the system at 7.8-8.5 during the addition process. After the addition is complete, continue to keep the temperature and react for 30-60 minutes to obtain acrylic copolymer emulsion. ⑤ Cool down to 76℃, slowly add silane mixture dropwise, maintain the pH of the system at 7.8-8.2 during the dropwise addition, continue to keep the temperature and react for 10-20 minutes after the dropwise addition is complete, then slowly add nano dispersion dropwise, raise the temperature to 85℃ after the dropwise addition is complete, and keep the temperature and react for 2-3 hours after the dropwise addition is complete. ⑥ Cool to 40℃, add 3-3.4 parts by weight of defoamer, stir and mix evenly, then add 3-3.4 parts by weight of preservative, stir and mix evenly, filter, and mature to obtain organosilicon acrylic hybrid emulsion.

7. The method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste according to claim 1, characterized in that, In step e), the lubricant is a stearate lubricant.

8. The method for preparing iron-silicon-aluminum magnetic powder cores using silicon steel waste according to claim 1, characterized in that, In step f), the annealing temperature is 600-800℃ and the annealing time is 1-3 hours.

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